The present invention relates to an electric actuator control apparatus or a reciprocative drive apparatus having an electric motor for opening or closing a valve at a plant or a water gate in electric power facilities with the electric motor.
When foreign substances are caught in opening-closing part of a valve or a water gate to increase load torque abnormally, an electric actuator detects abnormal increase in torque to stop the motor automatically.
FIG. 5 illustrates an example of a known electric actuator control apparatus in which an electric motor "A" reciprocates a load shaft "C" in an axial direction via a worm gear "B". By spline engagement, a worm "D" in the worm gear "B" does not rotate around a main shaft "E" which rotates via a gear by the electric motor "A", but moves in an axial direction. At the center of a worm wheel "F" which engages with the worm "D", is fixed a nut "G" which engages with a thread formed around the load shaft "C", and by rotating the worm wheel "F", the nut "G" actuates the load shaft "C". There are provided compression springs "H.sub.1 " and "H.sub.2 " between each end of the worm "D" and proper fixed members "I", whereby the worm "D" moves axially with thrust against the compression springs "H.sub.1 " and "H.sub.2 ".
The rotation of the main shaft "E" is transmitted via gears "J.sub.1 " and "J.sub.2 " to a drive gear "L" of gear counters "K.sub.1 " and "K.sub.2 ", which counts how many times the main shaft "E" rotates. The gear counters "K.sub.1 " and "K.sub.2 " comprises switches "M.sub.1 " and "M.sub.2 " which turns "ON" or "OFF" with respect to a preset counting value. If the load shaft "C" is of a valve, the switches "M.sub.1 " and "M.sub.2 " turn "ON" or "OFF" at a full-opening position and complete-closing position of the valve respectively. The gear counters "K.sub.1 " and "K.sub.2 " are adjusted to allow the switches "M.sub.1 " and "M.sub.2 " to be "ON" or "OFF" at full-opening and complete-closing positions respectively, the adjustment being made actually at full-opening or complete-closing situations of the valve.
Also, when a control signal is required to generate t an intermediate opening position, an intermediate gear counter (not shown) similar to the gear counter "K.sub.1 " and "K.sub.2 " may be connected with the drive gear "L". The valve is set to take a certain intermediate opening degree at which the intermediate gear counter is actually adjusted such that the switch turns "ON" or "OFF". At one end of the worm "D", there is provided an annular groove "N", which engages with a lever "O" rotatably secured to a proper fixed member. The lever "O" is connected to switches "P.sub.1 " and "P.sub.2 " which turns "ON" or "OFF" depending on a rotational angle.
The switch "P.sub.1 " turns "ON" or "OFF" when the electric motor "A" rotates in a forward direction (for example, the worm "D" is rotated in an opening direction of the valve) to produce resistance on the load shaft "C" so that the worm "D" moves axially to reach to a certain distance. The switch "P.sub.2 " detects movement of the worm "D" and turns "ON" or "OFF" when the electric motor "A" reverses. Since axial movement of the worm "D" is proportional to load torque, the switches "P.sub.1 " and "P.sub.2 " also work depending on load torque. The switches "M.sub.1 ", "M.sub.2 ", "P.sub.1 " and "P.sub.2 " control an electromagnetic switch "R" which connected to a power source "Q" for the electric motor "A". The switches "M" and "M.sub.2 " stop the electric motor "A" when the valve opens or is closed completely, while the switches "P" and "P.sub.2 " stop it when abnormal torque generates during opening or closing of the valve.
Opening degree of the valve is displayed by rotating a pointer "S" in an opening-degree indicator "T" depending on rotation of the main shaft "E". The opening degree is transmitted to a central supervision system via an angle signal generator "U" which converts rotational angle of the pointer "S" to an electric signal.
The known electric actuator for opening and closing a valve, a water gate, etc. requires operation at full-opening and complete-closing points of a valve and at maximum limit of abnormal load torque, but, to detect the operation points, a complicate structure as above is required, so that the number of parts increases. When an intermediate opening degree of a valve, etc. requires an operation point, one gear counter is required for one operation point, so that there are problems about connection of the gear counter with a main shaft and a storage space. Further, driven material such as a valve and a water gate operated by an electric actuator has different rotational angle of the rotation lever "O", the angle corresponding to operation stroke and load torque being variable depending on types and how to open and close a valve etc., and even the same product involves errors in each stroke and rotation angle, so that each operation point requires to be adjusted actually, which is troublesome and complicate.
The structure for detecting operation points is likely to result in a timing error due to wear at connection of gears, a lever, etc., and wear is different depending on frequency of reciprocating. So, in a plant where a number of electric actuators are used, terms for maintenance, inspection and part replacement are different in each actuator to involve troublesome work.
The switches "M.sub.1 ", "M.sub.2 ", "P.sub.1 " and "P.sub.2 " are integrally connected to the gear counters "K.sub.1 " and "K.sub.2 ", the rotation lever "O", etc., so that it is necessary to replace the whole control structure when contact points of each switch "M.sub.1 ", "M.sub.2 ", "P.sub.1 " and "P.sub.2 " are subject to wear and it is also necessary to adjust operation points when replaced. However, it is very difficult to operate a valve experimentally at full-opening and complete-closing positions while the plant is in operation. And it is impossible to adjust it by actual fitting.